Karen Rosenfelt, who worked with Frankel on “Marley” and “The Devil Wears Prada,” is producing through her Sunswept Entertainment banner.

Warner acquired bigscreen rights to “Septimus,” Angie Sage’s seven-book series, two years ago. “Septimus Heap: Magyk” revolves around two babies switched at birth, a boy who’s the seventh son of a seventh son and a girl destined to be a princess.

Brit author Sage, who wrote the series for HarperCollins, is exec producing. The first book, “Septimus Heap: Magyk,” was published in 2005, and three others have since been published, with the fifth, “Syren,” due out in September.

Frankel is repped by WME and Industry Entertainment; Lieber’s repped by UTA and Anonymous Content.